Abstract Tubular proteinuria resulting from impaired endocytic uptake of filtered proteins by the kidney proximal tubule (PT) is a common feature of early kidney dysfunction that poses a significant risk for development of end-stage renal disease. This proposal aims to understand the mechanistic basis of Dent disease, a progressive genetic disorder characterized by tubular proteinuria that is caused by mutations in the 2Cl-/H+ exchanger ClC-5. Enhanced degradation of megalin, a multiligand co-receptor that binds to filtered proteins, is thought to underlie the tubular proteinuria in Dent disease, however, the step in trafficking that is affected is unknown, and the contribution of pH vs. Cl- homeostasis to the disease phenotype is disputed. We will utilize a combination of genetic, morphological, mathematical modeling, and biochemical approaches to accomplish the following aims: (1) identify the step(s) in membrane traffic that are impaired in ClC-5 knockdown PT cells; (2) determine the molecular mechanism that links loss of ClC-5 to reduced megalin expression; and (3) identify therapeutic targets for restoring megalin expression and function in a mouse model of Dent disease.